1. Field of the Invention
The present invention relates to a surveillance system, and in particular, to structure for detecting an intruder and an intruding object in a surveillance system which embeds a camera and continuously monitors an intruder and an intruding object day and night into a controlled area such as an airport or a power plant.
2. Description of the Related Art
Up to now, in controlled areas such as an airport, a power plant, and a special building and a facility, and ecology investigations of nature animals, the detection of an intruder and an intruding object, where an infrared sensor has been used, surveillance (observation) by camera photographing, analyses of images photographed with a camera, and the like have been performed. Then, the transmission and reception of an infrared ray is performed by a pulse count system, a modulation frequency switching-system, or the like in the above-mentioned infrared sensor.
FIG. 9 shows the structure of the above-mentioned pulse count system. In this pulse count system, nine types of signals (1P to 9P) where one to nine pulses are inserted respectively in a period of 20 ms as shown are formed. Then, these nine types of infrared pulses are used as transmission and reception signals for surveillance.
FIG. 10 shows structure at the time of installing six pole-like main bodies Q1 to Q6 in a surveillance area. In this case, three types of infrared signals 1P, 2P, and 3P are transmitted and received by infrared sensors (floodlighting elements and photodetector elements) located at three locations in a vertical direction between main bodies Q1 and Q2. Similarly, three types of infrared signals 4P, 5P, and 6P are transmitted and received between main bodies Q2 and Q3, and three types of infrared signals 7P, 8P, and 9P are done between main bodies Q4 and Q5. Then, in a photodetection side, types of signals are identified by counting numbers of pulses within 20 ms as shown in FIG. 9, and it is judged whether they are the infrared signals (1P to 9P) assigned to detecting locations. Existence of an intruder or an intruding object is detected by whether the corresponding infrared signal is received. That is, when the assigned infrared signal is unreceivable, it is judged that an intruder etc. exists.
In the above-mentioned, a reason why the infrared rays whose signals (pulse number) are different are used is to avoid the interference of the infrared signals which are transmitted and received. Namely, since each of the infrared rays which are transmitted and received has a certain amount of divergence and further the above-mentioned main bodies Q1 to Q6 are installed with having a space of nearly 100 m, an infrared ray Lg outputted from an upper floodlight element of the main body Q5 of FIG. 10(A) is received with middle and lower photodetector elements of the main body Q6. Then, even if it is the upper infrared ray signal, if infrared signals which are transmitted and received by the upper to lower infrared sensors are the same, it is misdetected as being the infrared rays from the middle and lower photodetector elements. Hence, the existence of an intruder H1 is not detected, and therefore, an alarm failure (an alarm is not given in spite of an intruder entering) arises. However, as shown in FIG. 9, if the infrared rays (signals 4P to 6P) used in upper to lower steps are what can be identified, it is possible not only to avoid interference, but also to prevent the alarm failure.
Nevertheless, a conventional pulse count system has a problem that a false alarm (an alarm is given in spite of no intruder) and an alarm failure arises since a number of pulses which is counted is affected by sunlight which is extraneous light, direct projection of vehicle headlight etc., reflection of these extraneous light from an object, or reflection, wraparounds, and interference (noise) of infrared rays used for transmission and reception.
Namely, when an unnecessary pulse “a” is added by extraneous light etc. at the time of receiving an infrared ray of the signal 1P in FIG. 9, a received signal results in an infrared ray of the signal 2P. When a pulse “b” is removed under the influence of extraneous light etc. at the time of receiving an infrared ray of the signal 9P, a received signal results in the signal 8P. Hence, these lead to false alarms. In addition, when one or two of unnecessary pulses “a” are added when an infrared ray of the signal 4P floodlighted from the main body Q5 in FIG. 10(A) is received by a signal 5P or 6P infrared photodetector unit of the main body Q6, an alarm failure arises since the intruder H1 is not detected.
In addition, since this kind of surveillance system includes the outside of a building as a surveillance area in many cases, infrared light intensity is set high so as to be able to perform infrared transmission and reception even when there is an environmental change such as rainfall or snowfall, or fogging. Hence, this causes a false alarm or alarm failure. For example, since infrared rays of the main body Q1 in FIG. 10 also reach the main bodies Q3 to Q6 besides the main body Q2, this causes a false alarm.
Furthermore, the conventional pulse count system identifies only nine types of signals, and in addition, the modulation frequency switching system identifies only four types of signals. Hence, there is a problem that it is not possible to perform effective detection since there are few identifiable signals. That is, as shown also in FIG. 10, since nine types of infrared rays of signals 1P to 9P are altogether assigned in a region of main bodies Q1 to Q4, the same pulse signals 1P to 6P are used in the main bodies Q4 to Q6. Accordingly, when an infrared ray of the signal 1P of the main body Q1 reaches a photodetector unit of the main body Q5 by a wraparound etc., this leads to an alarm failure.
Then, up to now, without floodlighting from a floodlighting element straightly to a photodetector element like an infrared ray Lg (optical axis) shown by a dotted line in FIG. 10(B), the optical axis is turned a little in across wise direction like an infrared ray Lg (optical axis) shown by a continuous line. However, even if an infrared optical axis is turned in this way, it becomes hard to prevent the influence to the other main bodies when the main bodies Q1 to Q6 are installed nonlinearly, or when being installed in the neighborhood of a building etc.
FIG. 11(A) shows the case that the main bodies Q1 to Q6 are installed nonlinearly, and in this case, since an infrared ray has the certain extent of divergence, the infrared rays of the signals 1P to 3P floodlighted from the main body Q1 result in being received by the main body Q5 (chain double-dashed line in the diagram). In addition, FIG. 11(B) shows the case that the main bodies Q1 to Q6 are annularly installed near buildings B1 and B2. In this case, infrared rays of the signals 4P to 6P floodlighted with divergence (and with an optical axis being turned) from the main body Q2 are received by the main body Q6 after being reflected on the building B1. At the same time, infrared rays of the signals 7P to 9P floodlighted with divergence (and with an optical axis being turned) from the main body Q3 are received by the main body Q1 after being reflected on the buildings B1 and B2. Since becoming a cause of a false alarm or an alarm failure, this interference of infrared rays should be avoided.
Furthermore, up to now, since there are few types of identifiable infrared rays, only two to three infrared sensors are provided between main bodies. Hence, there may be the case that it is not possible to effectively detect an intruder H2 who invades with crawling as shown between the main bodies Q4 and Q5 in FIG. 10(A).
The present invention is made in view of the above-described problems, and aims at providing a surveillance system which can decrease the occurrence of false alarms and alarm failures remarkably by removing the influence of extraneous light and noise as much as possible, and making it possible to set a large number of identifiable signals.